Known antivibration devices typically comprise means for attaching to external elements, for instance between a vehicle chassis and its engine, and at least one damping means for supporting loads and damping vibration imparted therebetween.
With these types of antivibration devices, it is usually desirable to minimise the stiffness and damping in order to, in automotive applications for example, improve passenger comfort during certain operational and environmental events requiring isolation of vibrations of relatively high frequency, such as engine idling.
However, other operational and environmental events require high stiffness and damping, for example during engine cruise conditions, where the vibrations to be treated are mostly of low frequency and large amplitude due to the uneven surface of the road.
Conventional antivibration devices are not adapted to suitably damp multiple events as a stiff device is not desirable for vehicle conditions requiring high isolation and a relatively soft device is not desirable for vehicle conditions requiring motion control: the result is thus usually a compromise of all performance parameters.
Document U.S. Pat. No. 6,386,527 discloses a hydraulic antivibration device able to efficiently control stiffness and damping at specific frequencies using fluid resonance effects through constricted passages.
While this adequately addresses operation at the resonant frequency, it produces a sometimes undesirable increase in dynamic stiffness for frequencies above the resonant frequency